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Plants and animals conquer land

470 million years – 470 metres

Liverworts and arthopods were the first to rise up from the sea. (Walter Myers)

Liverworts and Arthropods rise to the dry land as first plants and land animals. Due to a collision of asteroids, the Earth is subjected to a powerful meteorite shower. It does not cause large-scale extinction, but accelerates the evolution of new species in the Baltic and other seas.

Kuva: First plants were liverworts and first land-animals millipede-like arthropods. Walter Myers

Ordovician period

First land-animals where millipede like Arthropods. The oldest fossils are 460 million years old. The transition was fascilitated by jointed exosceleton that allowed locomotion without the support of water. Around the same time land plants had evolved from green algae. 472 years old fossiles have been found from Argentina. Terrestrial life gave two benefits for plants: more efficient gas exchange and photosynthesis. However, the availability of water was limited and gravity hindered the vertical growth. Liverworts didn’t grow high, but had the protective surface layer (cuticula) that prevents desiccation.

A collision occured in the asteroid belt, between Jupiter and Mars. This caused a large amount of meteorites to hit the Earth. The closest evidence can be found in southern Sweden in the southern edge of the Vättern Lake, in Kinekulla. There are a lot of meteorites found in the layers of limestones. Life in the shallow sea was very diverse, and it seems that the shower of meteorites only speeded up the diversification of species, instead of slowing it down. The climate on the Earth was warm and the sea-level high, but climate was starting to cool.

Early Arthropod trackways at sandstone. Image: MacNaughton et al, Geology, 2002

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